P09.01.B MONITORING ACUTE CHANGES IN BRAIN ACTIVITY IN RADIOTHERAPY PATIENTS USING FNIRS

Abstract BACKGROUND Radiotherapy is a common treatment used for brain tumors, but it can lead to cognitive dysfunction years after the treatment. Recent studies have demonstrated that early functional alterations in the brain, which appear well before morphological changes, may predict later brain dysfunction. Thus, detecting these early functional changes is crucial to prevent complications. However, studies of immediate changes in brain function, occurring within minutes after irradiation, are scarce. Our aim was to investigate these acute effects of radiotherapy on brain function using functional near-infrared spectroscopy (fNIRS). MATERIAL AND METHODS We used fNIRS to study the acute effects of brain radiotherapy on a minute time scale. The technique monitors changes in oxygenated (HbO), deoxygenated (HbR), and total (HbT) hemoglobin, as well as water and cerebrospinal fluid (CSF) concentrations in the brain cortex. Measurements were done with optical sensors placed on a patient’s forehead for five minutes right before and after a treatment fraction. With fractionated treatments, measurements were taken during multiple treatment fractions. Patients received radiation doses of 2, 6, 9 or 20 Gy per fraction, according to their clinical treatment plan. We used fNIRS method to record changes in fractional amplitude of physiological pulsations (AF), modified from fractional amplitude of low frequency fluctuation (fALFF), in very-low (VLF, 0-0.1 Hz), respiratory (0.1-0.6 Hz) and cardiac (0.6-5 Hz) frequencies. This measure reflects regional brain activity. RESULTS Recordings were taken from 8 brain tumor patients (4 female, age 54 ± 14 years). For the analysis, 15 pre- and post-radiotherapy fraction recordings were used. These initial results show that the averaged AF value is lower within VLF and respiratory frequencies following radiotherapy, compared to prior recordings, suggesting a rapid reduction in regional brain activity. The AF value was statistically significantly lower in VLF for HbO and water (p <.05) signals, and in respiratory frequencies for HbO (p <.05), HbT (p <.01), and CSF signals (p <.05). Our results also indicate a slight, but statistically insignificant, increase in AF value in cardiac frequency. CONCLUSION Our preliminary findings suggest that radiotherapy induces a measurable decrease in brain activity within minutes post-irradiation. Understanding rapid changes in brain function could lead to better prevention strategies for cognitive dysfunction in patients undergoing radiotherapy. Support/Disclosure: We offer our thanks to the funders of this study: State Research Funding (VK and JN), Thelma Mäkikyrö Foundation (VK), Finnish Cultural Foundation (HM), and Tauno Tönning Foundation (HM).